The present invention relates to apparatus for drying sheets or strips of flexible material, and more particularly to improvements in apparatus for reducing the moisture content of sheets or strips of photosensitive material such as photographic films, photographic paper or the like. Still more particularly, the invention relates to improvements in apparatus for drying sheets or strips of photosensitive material (hereinafter called sheets for short) while the sheets are contacted, at both sides, by driven rollers and while the sheets are subjected to the action of a fluid medium which is caused to impinge against both sides thereof.
Apparatus for drying sheets of photosensitive material while the sheets are transported by driven rollers and are acted upon by streams of a hot gaseous fluid are disclosed, for example, in German Auslegeschrift No. 2,615,905 and in German Pat. No. 2,153,752. The rollers which advance the sheets along a path extending between two sets or groups or rollers are mounted on shafts which are driven by a motor or the like. The neighboring shafts at each side of the path for the sheets are so closely adjacent to each other that, if the leader of a sheet which is caused to advance through the drying or moisture expelling zone is engaged by a row of rollers on a first shaft and is directed against the rollers on the next-following shaft, the plane of the leader makes an acute angle with the plane which is tangential to the rollers and disposed between the two sets or groups of rollers. This ensures that the rollers on the next-following shaft can direct the leader back into the ideal path and on toward the peripheries of the rollers on the next-following shaft, and so forth. A drawback of such drying apparatus is that the shafts at each side of the path for the sheets to be dried are very closely adjacent to each other in order to guarantee that the actual path along which the sheets move is a meandering path sloping alternately toward a row of rollers at one side of the path, thereupon toward a row of rollers at the other side of the path, again toward a row of rollers at the one side of the path, and so forth. The degree to which the path meanders depends on the extent to which the rollers at one side of the path extend beyond the ideal path for the sheets, i.e., beyond a plane which is tangential to the rollers of the group or set of rollers at the other side of the path. While the mounting of a group of neighboring shafts at each side of the path exhibits the advantage that the configuration of a meandering path (if such path is desired or necessary) can be regulated within a narrow range, the drawbacks of such drying apparatus outweigh the advantages because the closely adjacent shaft and the rows of rollers thereon provide little room for admission of a gaseous moisture expelling fluid and for evacuation of moisture-laden fluid from the region of advancement of successive sheets through the apparatus. As a rule, the gaseous fluid is hot air which is blown against both sides of a moving sheet. Proper drying of a sheet in such apparatus can be accomplished only by unduly extending the path along which the sheets move through the drying zone. This contributes to space requirements of the drying apparatus as well as to the initial and maintenance costs. Apparatus of the type to which the present invention pertains may constitute integrated or separable units of production lines in photographic processing laboratories wherein exposed but undeveloped customer films are removed from cassettes or analogous containers, spliced together to form relatively large rolls of coherent films, transported through a developing machine, dried by exposure to hot air or another suitable gaseous fluid, and conveyed through a printing or copying machine if the customers desire to obtain prints of all or selected film frames.
A further drawback of presently known drying apparatus of the above outlined character is that, if the leaders of discrete sheets or strips exhibit a strong tendency to curl, they are likely to penetrate into the spaces between neighboring shafts at the one or the other side of the path with the result that the sheets or strips are deformed, defaced or totally destroyed. Such penetration of curling leaders of sheets or strips will take place even if the neighboring shafts at both sides of the path are very closely adjacent to each other, i.e., if the neighboring shafts are so close to each other that there is little room for installation of adequate nozzles which admit hot gaseous fluid and/or for removal of moisture-laden gases from the region of the path.